The present invention relates generally to apparatus for sampling the output of a laser source delivering laser-radiation via an optical fiber. The invention relates in particular to a laser source including a lens directing primary output into a first optical fiber and sampled output into a second optical fiber.
In many commercially available laser-radiation sources including a semiconductor laser, an array of semiconductor lasers, or a miniaturized diode-pumped solid-state laser for generating laser-radiation, the lasers or arrays are often packaged in a robust housing from which the laser-radiation is delivered via an optical fiber. This optical fiber is often referred to as a xe2x80x9cpigtailxe2x80x9d by practitioners of the art. The housing includes a lens for focusing (coupling) the laser-radiation into the optical fiber and may include other optical or electrical components depending on the type of laser or array.
Semiconductor lasers used in such a light source include edge-emitting diode-lasers and arrays thereof, electrically-pumped, vertical-cavity, surface-emitting lasers (VCSELs), and optically-pumped semiconductor (OPS) lasers using surface emitting semiconductor gain structures. Components included in the housing in addition to the focusing lens may include beam-shaping optics or, in the case of OPS or miniaturized solid-state lasers, diode-lasers for optical pumping. The housing is typically hermetically sealed and the optical fiber delivering the laser-radiation exits the housing via a sealed feedthrough.
In applications using such a laser-radiation source, it is often necessary to sample the delivered radiation. This may be required, for example, to monitor power of the radiation or to monitor the wavelength of the laser-radiation for tuning or wavelength-locking the source.
One commonly used method of sampling radiation from the delivery optical fiber of such a light source is to provide a tap on the optical fiber. This is typically done using a fused optical-fiber coupler. Such a coupler is relatively expensive, particularly if the polarization integrity of the laser-radiation must be preserved. Depending on the type of laser-radiation source, the cost of providing such a polarization-preserving tap may be as much as fifty percent of the source itself.
In some packages monitoring devices are included within the package. Sampling of the beam is effected by mirrors or the like within the package. Space restrictions within a package and environmental control issues, however, can limit the effectiveness of such devices.
There is a need for an inexpensive method of sampling the output of an optical fiber delivered light source. The method preferably should allow the sampled output to be used by devices located outside a package in which the source is housed.
The present invention is directed to a laser-radiation source delivering a main laser-radiation beam via one optical fiber and an auxiliary laser-radiation beam, of lesser power than the main laser-radiation beam, via another optical fiber. In one aspect, the inventive laser source comprises a laser delivering an output beam of laser-radiation, a lens, and two optical fibers. An optical arrangement is provided for dividing the output laser-radiation beam into the main laser-radiation beam and the auxiliary laser-radiation beam. The lens couples the main laser-radiation beam into an entrance face of one of the optical fibers, and couples the auxiliary laser-radiation beam into an entrance face of the other of the optical fibers.
The beam-dividing arrangement is located between the laser and the lens. Preferably, the optical fiber into which the main beam is coupled (the main optical fiber) is located with the entrance face thereof on an optical axis of the lens and spaced apart from the lens on a side thereof opposite the beam-dividing arrangement. The optical fiber into which the auxiliary beam is coupled (the auxiliary optical fiber) is preferably located adjacent the main optical fiber with the entrance face of the auxiliary optical fiber laterally spaced apart from the optical axis, and spaced apart from the lens by about the same distance as the entrance face of the main optical fiber. The optical fibers are preferably spaced apart from the lens by about one focal length thereof.
In one embodiment of the inventive laser source, the optical dividing arrangement is a wedge of a transparent material having entrance and exit surfaces located in the path of the output laser-radiation beam. The output laser-radiation beam is transmitted through the entrance surface of the wedge such that it is incident on the exit surface thereof. A portion of the entrance-surface-transmitted laser-radiation beam is transmitted through the exit surface of the wedge to provide the main laser-radiation beam. Another portion of the first-surface transmitted laser-radiation beam is reflected from the exit surface of the wedge and a portion of the exit-surface-reflected portion is reflected from the entrance surface of the wedge and transmitted through the exit surface of the wedge to provide the auxiliary laser-radiation beam. The main laser-radiation beam, on exiting the wedge, propagates generally along the optical axis of the lens, and the auxiliary laser-radiation beam, on exiting the wedge, propagates at an angle to the optical axis of said lens.
In another embodiment of the inventive laser source, the optical dividing arrangement includes a plate of a transparent material and a mirror. The plate has an entrance surface and an exit surface and is located on the optical axis of the lens and inclined thereto. The plate and the mirror are arranged such that a first portion of the output laser-radiation beam is transmitted through the plate to provide the main laser-radiation beam. A second portion of the output laser-radiation beam is reflected from the plate onto the mirror and reflected the mirror through the plate to provide the auxiliary laser-radiation beam. The main laser-radiation beam, on exiting the plate, propagates generally along the optical axis of the lens. The auxiliary laser-radiation beam, on exiting the plate, propagates at an angle to the optical axis of the lens.
In another aspect of the present invention, the laser, the lens, and the optical dividing arrangement are located in an enclosure. The entrance ends of the main and auxiliary optical fibers are located within the enclosure. The optical fibers extend through a wall of the enclosure for delivering the main and auxiliary laser-radiation beams from the enclosure.
An advantage of the inventive laser-radiation source compared with prior art fiber-delivered laser-radiation sources is that a sample of the laser-radiation is provided by an auxiliary optical fiber separate from the main (delivery) optical fiber, thereby avoiding a need to tap a delivery fiber to obtain a sample of the laser-radiation. A lens that would be required in any case to couple the laser radiation into the main optical fiber also couples a sample of the radiation into the auxiliary optical fiber. This minimizes the cost of providing the laser-radiation sample. Those skilled in the art will recognize other embodiments and advantages of the present invention from the detailed description of the invention presented hereinbelow.